An apparatus of the aforementioned kind is described in German patent application P 42 07 286.7. Liquid or plasticized material to be injected is transported in a cylinder sloped by 45.degree. relative to the axis of injection or to the axis of the conveying screw. A non-return valve at the mouth of the cylinder prevents the material from flowing back again into the screw cylinder during the shot sequence. The material introduced into the cylinder is injected into the mold cavity with the aid of a piston through the injection nozzle. The material conveyed by the screw is deflected into the cylinder by a heart-shaped groove. Even though good results can be obtained with this apparatus for shots weighing up to 0.2 grams, the apparatus has some drawbacks.
One drawback is that the non-return valve denotes a weak point, especially when processing materials of low viscosity, because the closing movement of the non-return valve triggered by the injection movement has only an inadequate sealing effect.
Furthermore, the prior art apparatus exhibits poor flow cross sections. Because the material flows around the injection piston by way of the heart-shaped groove section, an unnecessary shear of the material takes place due to the piston during the injection process. In addition, the production of this apparatus is expensive and complicated.
Therefore, the present invention is based on the problem of designing an injection unit of the aforementioned kind in such a manner that a uniform flow of the material from the material feed system, by way of an injection cylinder, to the nozzle is guaranteed. Likewise, the present invention is based on the problem of providing for the manufacture of a simple unit.